This invention relates to fluid seals, and more particularly to such seals capable of functioning under dynamic as well as static conditions to prevent leakage of any fluid, corrosive or non-corrosive, throughout a wide temperature and pressure range, and especially following subjection to a fire.
In the oil and gas industry, due to encountering more corrosive well conditions, higher pressures and increasing temperatures, requirements have arisen for better and safer seal systems for use in oilfield equipment. The prior art is replete with descriptions of static seals for preventing undesired escape of fluids, both corrosive and non-corrosive, to the environment at widely ranging temperatures and pressures, and of dynamic seals also designed to function under somewhat similar adverse conditions. Although many of these known seals have been employed successfully, they all have one or more limitations that preclude satisfactory performance under a combination of unusual and relatively extreme conditions that are presented when, for example, the seal is employed between the rotatable stem and the bonnet of a valve on an oil or gas well christmas tree, and the tree is involved in a fire. In such a circumstance, if the seal is of elastomeric or other non-metallic construction the fire destroys it, usually resulting in grave or even disastrous consequences. If, on the other hand, the seal is all-metallic it may function satisfactorily in a static condition, but the high friction forces created when the seal is forced into fluid-tight contact with the stem and the bonnet or other surrounding metal surface prevent rotation of the stem and thus movement of the valve's flow control element between open and closed positions.
Accordingly, there exists a need for a fire-safe metal-to-metal seal system that will function both statically and dynamically to prevent the escape of corrosive and other fluids over a wide range of temperatures and pressures, and that will not unmanageably restrict relative movement of the valve or other elements between which the seal functions. It is to satisfy this need that the present invention is directed.